The present invention relates to shell and tube heat exchangers and, in particular, to an arrangement for marking specific tubes, for example tubes that need to be repaired, serviced differently than other tubes, left alone or otherwise corrected. Shell and tube heat exchangers that are used as chemical reactors may have many thousands of open-ended tubes. Various methods have been used in the past to mark tubes. Usually, a marker cap has been inserted into the open end of the tube being marked, but those markers can come loose when people walk on top of the tube sheet, and they require the marker to be removed in order to treat the tube. Also, when the marker is removed in order to treat the tube, the location of the tube may be lost. Other methods of marking tubes have included using paint, tape, and permanent markers on the tube sheet. However paint, tape and ink can rub off as people walk along the tube sheet.
One or more of the tubes in the chemical reactor may have thermocouples to monitor the reaction temperature during operation. The catalyst in these thermocouple tubes is loaded separately with special attention to the thermocouples and their electrical leads. It is useful to be able to temporarily seal a thermocouple tube to prevent catalyst loading in that tube while the other tubes are being loaded. Once the other tubes are loaded with catalyst, it is useful to be able to readily identify the thermocouple tubes to be separately loaded with catalyst but without obstructing the thermocouple tube to be loaded.